1. Field of the Invention
The present invention relates generally to a method and apparatus for receiving broadcast signals, and in particular, to a method and apparatus capable of improving performance of a hybrid terminal realized by integrating, into one terminal, a terminal of a mobile communication system (hereinafter mobile communication terminal) and a broadcast receiver for receiving broadcast signals.
2. Description of the Related Art
Digital broadcasting systems have been developed to provide ubiquitous high-quality audio and video services by means of fixed terminals or mobile terminals.
The digital broadcasting systems can be classified into Digital Audio Broadcasting (DAB), Digital Radio Broadcasting (DRS), Digital Audio Radio System (DARS) and Digital Multimedia Broadcasting (DMB) capable of supporting audio, video and data services.
Recently, the Digital Video Broadcasting for Handheld (DVB-H) system that has enhanced mobility and portability of the European Research Coordination Agency project-147 (Eureka 147) system, which is another example of the European DAB system, and the Digital Video Broadcasting-Terrestrial (DVB-T) system, which is one of the digital broadcasting standards, is now attracting the public attention. To reduce power consumption of the portable terminal, DVB-H adopts the so-called Time Slicing Multiplexing scheme, which is for slicing a broadcast signal into time slots for individual channels, and carrying packetized broadcast signals of the individual channels over the time slots.
The recent digital communication system generally provides broadcast services, and the mobile communication system also tends to support not only the existing mobile communication services but also the broadcast services. Herein, the ‘mobile communication service’ should be construed to include the general voice call service, and the packet service such as Short Message Service (SMS). A hybrid terminal has also been developed, which is realized by uniting into one terminal a broadcast receiver of the broadcasting system and a terminal of the existing mobile communication system. For example, in Europe, a study is being conducted to develop a hybrid terminal realized by combining a DVB-T or DVB-H receiver as a broadcast receiver with a Global System for Mobile communications (GSM), Enhanced Data for GSM Evolution (EDGE), or Wideband-Code Division Multiple Access (W-CDMA) terminal as a mobile communication terminal.
One of the important matters that should be considered during the development of the hybrid terminal is how to design a structure of a Radio Frequency (RF) front-end unit of the terminal.
FIG. 1 illustrates the conceptual structure of a hybrid terminal supporting both a broadcast service and a mobile communication service.
Referring to FIG. 1, a hybrid terminal 100 includes a mobile communication terminal 110a and a broadcast receiver 110b in a single terminal 110, and is basically designed to transmit/receive (Tx/Rx) a broadcast service and a mobile communication service via different RF paths. The mobile communication terminal 110a includes an RF front-end unit 111 based on a Tx/Rx switching circuit or a duplexer. The hybrid terminal 100 transmits/receives mobile communication signals via a first ANTenna ANT1, and receives broadcast signals via a second ANTenna ANT2.
However, the hybrid terminal 100 with the structure of FIG. 1 may suffer from performance degradation due to the mutual signal interference between both signals because reception of the broadcast signal and transmission/reception of the mobile communication signal are performed in the single terminal. For example, the transmission signal of the mobile communication terminal 110a may serve as an interference signal to the received signal of the broadcast receiver 110b. 
FIG. 2 illustrates an example in which a broadcasting system and a mobile communication system use adjacent frequency bands. In this example, a DVB-H system is used as the broadcasting system, and a GSM system is used as the mobile communication system.
Referring to FIG. 2, a DVB-H signal 201, or broadcast signal, uses 470 to 862 MHz, and a GSM signal 203, or mobile communication signal, uses 880 to 915 MHz or 925 to 960 MHz, showing that they use adjacent frequency bands. Therefore, the broadcast signal may serve as a partial interference signal to the mobile communication signal. More particularly, in the opposite case, the terminal's transmission signal in the mobile communication signal may interference with the broadcast signal. That is, in the hybrid terminal 100 of FIG. 1, because the mobile communication terminal 110a is installed together with the broadcast receiver 110b, the transmission signal of the mobile communication terminal 110a may interference with the broadcast receiver 110b, thus causing noticeable performance degradation.
To solve this problem, one method prevents reception of the broadcast service in the frequency band adjacent to the frequency band of the mobile communication system, and another method adds in the broadcast receiver a filter capable of canceling the mobile communication signal.
The former method can hardly be implemented when the scarcity and value of the frequency band are considered. Since the latter method adds a filter to the terminal, it considerably increases the production cost of the terminal. Also, an increase in the side lobe component of the mobile communication signal may increase a scope of the adjacent frequency band affected by the mobile communication signal, so the interference of the in-band mobile communication signal of the broadcasted received signal may cause performance degradation of the broadcast receiver.
Therefore, there is a need for a new solution capable of minimizing the performance degradation due to the mobile communication signal during broadcast signal reception without increasing the production cost of the hybrid terminal.